Bone anchor assembly with pivotable retainer and independently rotatable shank

ABSTRACT

A polyaxial bone screw includes a head member and a shank member. The shank has a capture end and an opposite threaded end for threaded insertion into a vertebra. The head has a U-shaped cradle for receiving a spinal fixation rod and a central bore for receiving the capture end of the shank. An expandible retainer ring with a radial split is snapped onto the capture end of the shank to retain it within the head. The retainer ring has a spherical outer surface which forms a ball joint with a spherical socket cavity within the head to enable the head to be angled relative to the shank. A threaded closure plug is tightened within the cradle to clamp the rod into engagement with a knurled dome on the capture end of the shank to secure the rod relative to the vertebra.

BACKGROUND OF THE INVENTION

The present invention is directed to a bone screw of the type wherein ahead of the bone screw is swingable or can swivel about the shank of thebone screw until the surgeon is satisfied with the relative placement ofthe two parts and thereafter the head can be locked in position relativeto the shank. Such screws are also referred to as polyaxial head orswivel head bone screws, since the head can be positioned in any of anumber of angular configurations relative to the shank.

Bone screws are advantageously utilized in many types of spinal surgeryin order to secure various implants to vertebrae along the spinalcolumn. Bone screws of this type typically have a shank that is threadedand adapted to be implanted into a vertebral body of a vertebra. Thebone screw includes a head which is designed to extend beyond thevertebra and which has a channel to receive another implant. Typicallythe channel will receive a rod or a rod-like member. In bone screws ofthis type, the head may be open, in which case a closure must be used toclose between opposite sides of the head once a rod-like implant isplaced therein, or closed wherein a rod-like implant passes through thehead of a bone screw. Open head screws are most often used, mainlybecause it is difficult to feed long rods through closed head screws.

Bone screws are also available with heads permanently fixed relative toa shank or with polyaxial heads that initially swivel to allow placementand are then lockable in a desired positional configuration. When thehead and shank of the bone screw are fixed in position relative to eachother, it is not always possible to insert a bone screw into the bone insuch a manner that the head will be in the best position for receivingother implants. Consequently, the polyaxial head bone screws have beendesigned that allow the head of the bone screw to rotate or swivel aboutan upper end of the shank of the bone screw, while the surgeon ispositioning other implants and finding the best position for the bonescrew head. However, once the surgeon has determined that the head is inthe best position, it is then necessary to lock or fix the head relativeto the shank. Different types of structures have been previouslydeveloped for this purpose. Unfortunately, the prior art devices have atendency to be bulky, slip under high loading or require many parts.

It is desirable to have a polyaxial head bone screw that can be capturedby the shank prior to locking of the head, but that allows the head tofreely swivel or pivot about a top of the shank prior to locking. It isthen further desirable to have the head capable of being fixably lockedin a configuration or position relative to the shank where the head bestfits with other elements of the overall spinal implant.

As noted above, many prior art swivel type bone screws have a bulky andheavy structure. In spinal surgery, it is desirable to provide a lightweight implant that impacts on the surrounding tissue as little aspossible. Consequently, it is desirable to have a bone screw with a lowprofile with respect to both height and width. It is also preferable tolimit the width profile of the bone screw to provide more room to workalong a rod or other implant in which many elements may be required in arelatively small space.

Furthermore, it is desirable to maintain the number of parts of thedevice at a minimum. Also, it is desirable to secure the various partstogether in such a way, so that, if parts become loose under use forsome reason, the device will not totally disassemble.

SUMMARY OF THE INVENTION

The present invention provides an improved polyaxial head bone screwassembly for use in conjunction with spinal surgery and, in particular,for implanting into a bone and securing other medical implants to thebone. The polyaxial bone screw assembly includes a threaded shank memberfor threaded placement in a bone, a head member connecting to anotherimplant such as a spinal fixation rod and capturing a capture end of theshank member, and a retainer sphere or retainer ring to capture andretain the capture end of the shank member within the head member. Theshank member and head member may be set in a plurality of angularrelationships with respect to each other within a range of obtuseangles.

The shank or shank member has an outer portion which is threaded, sizedand shaped so as to be adapted to be operably screwed into a vertebralbody in the spine of a patient. An end of the shank opposite thethreaded lower portion includes a frusto-conical capture structure whichdiverges in diameter in a direction away from the threaded end of theshank. A top of the conical capture end is provided with apertures orformations for non-slip engagement by an installation tool to enable theshank to be threaded into a bone, such as a vertebra. Beyond the conicalstructure, a knurled dome is provided for positive interfering orcutting engagement by the surface of a rod which is to be clamped andsupported by the bone screw assembly.

The head member is generally partially cylindrical in outer shape andhas a central axial bore to receive the capture end of the threadedshank and a central U-shaped cradle opens in a direction opposite theaxial bore to receive a spinal fixation rod and presents a pair ofspaced apart arms. An interior of each of the arms includes threads toreceive a threaded plug to secure the rod within the cradle and to clampthe rod into engagement with the knurled dome of the shank to fix theangular position of the head with respect to the shank. The headincludes a lower partially spherical socket or seat at the lower end ofthe axial bore for receiving the ring and forms a neck for surroundingthe shank during usage.

The retainer ring has an outer surface which is partially spherical andwhich is sized and shaped to fit within and swivel within the seat untillocked in position, as noted below. The ring also has a central borewhich is frusto-conical and of a shape which is compatible with thecapture end of the shank to snugly receive the shank therein. The ringis sized to be too large in width to fit through the neck at the bottomof the head when in operable position and is either loaded from the topof the head or through other structure formed in the head. The ring isresiliently expandible to enable the ring to be snapped over the captureend of the shank to retain the capture end within the head member. Thehead has an assembly or orientation cavity therein which communicateswith the U-shaped cradle and which is positioned and sized to enableproper orientation of the retainer ring and engagement of it with thecapture end of the shank. The assembly cavity is spaced axially abovethe seat and neck and has a slightly larger partial spherical diameterthan the seat so as to allow the ring to expand during insertion of theshank capture end and then return to a smaller diameter for snuglyfitting in the seat. The spherical seat initially forms a pivot bearingwith the retainer ring, when no axial downward force is applied to theshank and ring, to retain the capture end of the shank within the headand to enable pivoting the shank relative to the head throughout alimited range. The retainer ring is formed of a resilient or springymaterial and in a preferred embodiment has a radial split to enableexpansion of the diameter of the ring and, particularly, to enableexpansion of the diameter of the central bore to enable placement on theconical capture end of the shank.

Once the ring is on the shank and located in the seat in a positionsuitable to the surgeon with a rod received in the head channel, aclosure plug is screwed into the threads between the arms so as toengage the rod and urge the rod under pressure into engagement with thedome on the shank. This in turn urges the spherical surface on the ringinto frictional engagement with the spherical surface of the seat so asto lock the rotational position of the shank relative to the head. Thedome of the shank is preferably radiused so that it engages the rod inthe same manner no matter what alignment is formed between the head andthe shank. The dome also preferably has a radius that is substantiallyless than the radius of the partial spherical surface of the ring. Thisreduces the required height of the head in comparison to the dome thatis a continuation of the spherical surface.

Preferably, the shank feeds into the head from below through the neck ofthe head and has a smaller diameter in the region of the capture endthan the diameter of the threads. This allows the shank to have acomparatively wide and normal thread for screwing into the bone that maybe wider than the neck of the head, while also allowing the top of theshank to pass through the neck of the head to connect with the retainerring.

In the present invention, because the retainer or retainer ring is widerthan the width of the rod receiving channel in the head, the ring ispreferentially less in height than the width of the channel such thatthe ring is turned sideways for loading and then turned again a quarterturn to reposition the ring in the head cavity to receive the shank. Fora comparable head designed to receive a rod of a certain diameter thisallows the retainer to have a greater width. This, in turn, allows theopening through which the shank passes to have a greater diameter andstill block passage of the retainer. Because the diameter of the openingis greater, the diameter of the neck and capture end of the shank canalso be sized greater allowing for greater strength and optionallyallowing the shank to be cannulated or axially bored to provide for useof a guide wire.

In an alternative embodiment, the shank capture end is an axiallyaligned cylinder that is received through a lower opening in the head. Ashank capture member or retainer is generally spherical in shape and hasat least a lower partial spherical surface for rotatably engaging amating surface in a cavity of a head of the bone screw. The sphericalshaped retainer has a pair of diametrically opposed side bores thatintersect with a bore that receives the shank capture end and whichprovide for the use of a crimping or deforming tool to pass through theretainer side bores so as to engage and deform the shank capture end.

The deformation of the shank capture ends interferes with removal of theretainer and locks or joins together the shank and retainer so that amain body of the shank protrudes outward from the opening in the bottomof the head and the retainer remains in inside the head on the oppositeside of the head lower opening which has a smaller diameter than theportion of the retainer that engages the cavity at the head loweropening, swivelably rotatably securing both the retainer and shank tothe head to allow a surgeon to position the head to receive the rod. Abore in the top of the retainer has faceted sides that produce a hex orother shaped opening for receiving a tool for driving the bone screwinto a bone or removing the bone screw. The retainer and shank arefurther locked against rotation when a closure is used to apply pressureto a rod member received in the head which in turn applies pressure tothe retainer and frictionally locks the position of the retainer in thecavity and the relative position of the shank to the head.

OBJECTS AND ADVANTAGES OF THE INVENTION

Therefore, the objects of the present invention include: providing animproved bone screw assembly for implantation into a vertebra of apatient wherein the head of the bone screw is swingable or swivelableabout an end of a shank of the bone screw until a desired configurationis obtained after which the head is lockable in position relative to theshank; providing such a screw assembly including a threaded shank with acapture end, a head member with a shank receiving bore and a U-shapedrod cradle for receiving a spinal fixation rod, a resiliently expandibleshank retainer or retainer ring to retain the capture end of the shankwithin the head, and a threaded plug receivable in the head to engage acradled rod and urge it into securing engagement with the capture end ofthe shank to fix the angular position of the shank relative to the head;providing such a screw assembly wherein the head member includes aninternal partial spherical cavity, socket or seat and the retainer ringincludes at least a partial spherical outer surface to enable swivelingand universal positioning of the shank relative to the head member fromside to side and front to rear within a limited range; providing such ascrew assembly in which the head member includes an assembly ororientation cavity above the seat to enable expansion of the ring duringjoining with the shank and proper orientation of the retainer ring;providing such a screw assembly in which the retainer ring has a radialsplit to enable resilient expansion and retraction of the ring forsnapping the ring onto the capture end of the shank; providing such ascrew assembly in which the capture end of the shank is frusto-conical,diverging in diameter in a direction away from the threaded part of theshank and in which the retainer ring has a central bore which iscompatibly frusto-conical in shape; providing such a screw assembly inwhich the capture end of the shank has a knurled dome for positive,interfering engagement by a spinal fixation rod clamped within theassembly and wherein the dome has a radius that is smaller than theradius of the ring partial spherical surface; and providing analternative bone screw utilizing a generally spherical retainer with abore for receiving a capture end of an associated shank after which theshank capture end is deformed so as to interferingly secure the shank tothe retainer; and providing such a polyaxial head bone screw which iseconomical to manufacture, which is convenient and secure in use, andwhich is particularly well adapted for its intended purpose.

Other objects and advantages of this invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged cross sectional view of a polyaxial head screwwith a split retainer ring which embodies the present invention, shownassembled with a rod to hold the rod and inserted in a vertebral bone.

FIG. 2 is an exploded perspective view of elements of the bone screw ata reduced scale and illustrates a threaded shank member, a head member,and a retainer ring.

FIG. 3 is an enlarged cross sectional view of the screw head andillustrates the orientation of the split retainer ring for insertioninto the head.

FIG. 4 is a view of the screw head similar to FIG. 3 and shows theorientation of the retainer ring to prepare for insertion of a captureend of a threaded shank.

FIG. 5 is a view similar to FIG. 3 and shows the retainer ring about tobe snapped onto the capture end of the threaded shank.

FIG. 6 is a view similar to FIG. 3 and shows the retainer ringpositioned on the capture end of the threaded shank.

FIG. 7 is a view similar to FIG. 3 and shows the capture end of theshank with the installed retainer ring positioned in a spherical pivotseat of the screw head.

FIG. 8 is a view similar to FIG. 3 and shows the threaded shank withretainer ring pivoted to a selected angle relative to the screw head.

FIG. 9 is an exploded perspective view of a second embodiment of apolyaxial bone screw in accordance with the present invention, showing ashank, a head and a partial spherical retainer.

FIG. 10 is an enlarged cross-sectional view of the head of the secondembodiment, taken along line 10-10 in FIG. 11.

FIG. 11 is an enlarged top plan view of the head of the secondembodiment.

FIG. 12 is an enlarged cross-sectional view of the head of the secondembodiment, taken along line 12-12 in FIG. 11.

FIG. 13 is an enlarged and fragmentary side elevational view of theshank, head and retainer of the second embodiment, showing the retainerbeing placed on the shank and raised relative to the head.

FIG. 14 is an enlarged and fragmentary cross-sectional view of theshank, head and retainer of the second embodiment with a crimping toolbeing utilized to deform the shank to interferingly secure the retainerand shank together.

FIG. 15 is a view similar to FIG. 14, but with the shank loweredrelative to the head and with the retainer seated in a partial sphericalchamber of the head allowing rotation of the shank and retainer relativeto the head.

FIG. 16 is an enlarged and fragmentary view of the shank, head andretainer, taken along a line similar to line 10-10 of FIG. 11 andshowing elements in the same position as FIG. 15.

FIG. 17 is an enlarged and fragmentary side elevational view of theshank, head and retainer, assembled as in FIG. 15.

FIG. 18 is an enlarged and fragmentary perspective view of the elementsof the bone screw shown in FIG. 17 being driven into a vertebra that isshown in cross-section by a driving tool.

FIG. 19 is an enlarged, exploded and perspective view showing theelements of the bone screw, as seen in FIG. 15 along with a closure andclosure set screw.

FIG. 20 is an enlarged front elevational view of the fully assembledbone screw of the second embodiment implanted in a vertebra shown incross section and showing a break-off head of the set screw having beenbroken away from a remainder of the set screw.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure.

Referring to the drawings in more detail, the reference numeral 1generally designates a polyaxial bone screw arrangement which embodiesthe present invention. The arrangement 1 includes a threaded shankmember 2 for threadably implanting into a bone 3, such as a vertebra,and a head member 4 which connects with the shank member 2 to engage andsecure a rod member 5, such as a spinal fixation rod, relative to thebone 3. The arrangement 1 also includes a retainer or retainer ring 7operably positioned within head 4 and engaging a capture end 9 of theshank 2 opposite a region having a thread 8 to retain the capture end 9within the head 4. The arrangement 1 further includes a plug or closuremember 10 which urges the rod 5 into engagement with the capture end 9of the shank 2. The head 4 and shank 2 cooperate in such a manner thatthe head 4 and shank 2 can be secured at any of a plurality of obtuseangles, relative to one another and within a selected range of anglesboth side to side and front to rear, to enable flexible engagement ofthe arrangement 1 with a rod 5.

Referring to FIGS. 1, 2, and 5, the shank 2 is elongated and is sizedand shaped to be screwed into one of the vertebra 3. The shank 2includes the external helically wound thread 8 that extends from anouter tip 12 to near the capture end 9. On the illustrated shank 2, thecapture end 9 includes a region that is frusto-conical in shape,diverging in diameter in a direction away from the outer tip 12 and thatis coaxially aligned with an axis of the shank 2. The illustratedcapture end 9 has a maximum radius that is substantially less than aradius associated with the shank thread 8 and further, preferably lessthan the radius of a body 13 of the shank 2 in the region whereupon thethread 8 is located.

The capture end 9 has a plurality of tool engageable grooves, aperturesor the like 14 to enable positive engagement by an appropriately shapedinstallation tool (not shown) to thread and drive the shank 2 into thevertebra 3. An upper end surface 16 of the capture end 9 opposite thetip 12 is provided with a formation or dome 18 to be positively andinterferingly engaged by the rod 5 when the assembly 1 is assembled intoplace. The illustrated shank 2 includes the dome 18 which is radiusedand knurled and that centered on the upper end surface 16 of the shankcapture end 9 so as to be coaxial with the remainder of the shank 2. Thescoring or knurling of the dome 18 operably frictionally abuts against acylindrical surface 20 of the rod 5, when the plug 10 is tightened toprovide non-slip engagement of the shank 2 relative to the rod 5 and tothereby help maintain a desired angular relationship between the shank 2and the head 4. In certain embodiments, the purpose of the dome 18 issimply to be engaged by the rod 5 during assembly and pushed in such amanner as to frictionally engage the ring 7 with the head 4 as describedbelow. Preferably, the dome 18 is radiused so that the dome 18 engagesthe rod at the same location even as the head 4 is swivelled relative tothe shank 2. However, in certain embodiments the dome 18 could haveother shapes.

Referring to FIGS. 2-8, the head member 4 is generally cylindrical inexternal profile and has a central and axially aligned shank receivingbore 24 ending at an inner and lower neck 26. The neck 26 is radiused toreceive the shank capture end 9 and preferably smaller than the radiusof the shank body 13 and thread 8. The bore 24 is also preferably sizedlarger than the capture end 9 of the shank 2 to enable the shank 2 to beoriented through a range of angular dispositions relative to the head 4.The bore 24 may be conically counterbored or beveled in a region 28 towiden the angular range of the shank 2.

The head 4 is provided with a U-shaped rod cradle 30 which is sized toreceive the rod 5 therethrough. The illustrated cradle 30 is rounded andradiused at an inner or lower portion 31 to snugly mate with the surfaceof the rod 5 and open at an outer end 33, with spaced apart parallelside surfaces 32 so as to form upstanding and spaced apart arms 35 withinwardly facing threading thereon. The side surfaces 32 have mating andguide structures 34 formed thereinto which are complementary to matingand guide structures 36 of the closure plug 10 (FIG. 1). The structures34 and 36 may be helically wound flanges or threads which advance theplug 10 into the head 4, as the plug 10 is rotated about its axis. It isforeseen that structures 34 and 36 may be V-shaped threads, buttressthreads, reverse angle threads, or other types of threads or flangeforms. Preferably, the structures 34 and 36 are of such a nature as toresist splaying of the arms 35 when the plug 10 is advanced into thecradle 30.

As seen in FIGS. 3 and 4, the head 4 has an assembly cavity 38 formedtherein which opens into the cradle 30. A partially spherical socket orseat 40 communicates between the assembly cavity 38 and the shank bore24 and has a radius that is slightly less than the radius of theassembly cavity 38 that is located axially directly thereabove. Thepurposes for the cavity 38 and seat 40 will be detailed further below.The head 4 may include external, closed end grip bores 42 for positiveengagement by a holding tool (not shown) to facilitate secure grippingof the head 4 during assembly of the arrangement 1. The seat 40 has aspherical radius and extends upward coaxially through the head 4 fromthe neck 26 to the cavity 38.

The closure plug 10 is generally cylindrical in shape and is providedwith a break-off head 44 which is connected to the plug 10 by a weakenedarea such that the head 44 separates from the plug 10 at a predeterminedtorque applied to the head 44 during assembly. The illustrated break-offhead 44 has a hexagonal cross section for engagement by a tool (notshown) of a complementary shape.

The retainer ring 7 is used to retain the capture end 9 of the shankmember 2 within the head member 4. The retainer ring 7 resilientlyexpands and contracts to enable the ring 7 to be snapped over and seatedon the capture end 9 of the shank 2. The ring 7, like the remainder ofthe arrangement 1, is preferably formed of a material such as a springstainless steel, tantalum, titanium or other resilient implantablematerial. The illustrated ring 7 has a radial split 48 which allows thering 7 to expand in circumference to fit over the capture end 9.Alternatively, other configurations of the ring 7 are envisioned toenable such expansion and retraction of the ring 7. The ring 7 has acentral conical bore 50 which is conically shaped to be compatible withthe conical shape of the capture end 9. The ring 7 has an outer surface52 which is frusto-spherical, partially spherical, or a segment of asphere, and which has a spherical radius approximately equivalent to thespherical radius of the spherical seat 40 within the head 4 and smallerthan the radius of the cavity 38. The ring surface 52 also has a radiussubstantially greater than the dome 18.

FIGS. 3-8 illustrate step by step assembly of the components of the bonescrew arrangement 1. In FIG. 3, the ring 7 is inserted into the head 4through the interior of the U-shaped cradle 30. The ring 7 is orientedwith its axis at a right angle to the axis of the bore 24 and to theside surfaces 32 of the cradle 30. FIG. 4 illustrates the ring 7oriented with its axis parallel or coincident with the axis of the bore24 and neck 26, by rotating the ring 7 within the assembly cavity 38. InFIGS. 5 and 6, the capture end 9 of the shank 2 is inserted through thebore 24 and engaged with the retainer ring 7 so as to snap the ring 7over the capture end 9. This is accomplished by pressing the shank 2into the head 4, causing the ring to engage a constriction at the top ofthe assembly cavity 38. The relative resistance encountered by the ring7 allows the capture end 9 to expand the circumference of the retainerring 7, by expansion of the split 48, so that the capture end 9 entersthe central bore 50 of the ring 7. The capture end 9 includes a shoulder56 which limits penetration of the capture end 9 into the retainer ring7, as shown in FIG. 6.

FIG. 7 shows the arrangement 1 with the retainer ring 7 lowered from theassembly position and positioned in the spherical seat 40 and thecentral axis of the shank 2 coaxial with the central axis of the head 4.FIG. 8 shows the shank 2 angled relative to the head 4. The sphericalseat 40 and spherical outer surface 52 of the retainer ring 7, whenseated in the seat 40, allows universal angular positioning of the shank2 relative to the head 4 within a limited range, as is shown in FIG. 8.The retainer ring 7, thus, performs the double functions of preventingthe capture end 9 of the shank 2 from slipping through the neck 26 and,in conjunction with the seat 40, forms a ball joint for relativeorientation of the shank 2 and head 4.

Under some circumstances, it may be desirable to assemble the shank 2and head 4, prior to threading the shank 2 into the vertebra 3 or otherbone. Thereafter, the shank 2 may be conveniently screwed into thevertebrae 3 by passing the installation tool through the cradle 30 toengage the grooves 14 of the capture end 9. The vertebra 3 may bepredrilled with a pilot hole or the like (not shown) to minimizestressing the bone 3. Once the shank 2 has been threaded to its desireddepth, the head 4 can be oriented as desired. The rod 5 is positioned inthe cradle 30, engaging the knurled dome 18, and the closure plug 10 isadvanced into the head 4 to clamp the rod 5 between the capture end 9and the closure plug 10. When the preset torque limit of the plug 10 isreached, the break-off head 44 separates from the closure plug 10. Theforce transmitted by torquing of the closure plug 10 transmits throughthe rod 5 and through the dome 18 to the ring 7. The partial sphericalsurface 52 of the ring 7 is thereby urged into tight frictionalrelationship with the partial spherical surface 40 of the head 4,thereby locking the angular configuration of the head 4 relative to theshank 2.

The reference numeral 100 generally represents a second embodiment of abone screw shown in FIGS. 9 through 20 in accordance with the presentinvention for implanting in a vertebra 101 or other bone.

The bone screw 100 includes a head 105, a shank 106, a retainer orcapture sphere 107 and a closure 108. The bone screw 100 also operablyreceives a rod member 110 that is part of an implanted assembly.

The head 105 has a lower body 115 with a pair of upstanding and spacedarms 116 and 117. The arms 116 and 117 are spaced sufficiently to form achannel 120 that is sized and shaped to snugly receive and subsequentlysecure the rod member 110 to the bone screw 100. In this manner thechannel 120 opens upward and sideways outwardly to opposed sides of thehead 105. The head 105 has a central axis indicated by the referenceletter A. The channel 120 has a pair of lower spaced curved surfaces 121that preferably have substantially the same radius as the rod member110.

An axially centered chamber 122 is located in the head 105 below thechannel 120 and opens upwardly into the channel 120. The chamber 122 hasa surface 125 that is sized and shaped to snugly but slidably receivethe sphere 107. In particular, a lower portion or hemispherical seat 126of the chamber surface 125 is curved or hemispherical so as to havesubstantially the same radius as the sphere 107.

An axially aligned bore 129 communicates between the chamber 122 and alower exterior of the head 105. The bore 129 has a smaller diameter thanthe sphere 107, so as to prevent passage of the sphere 107 through thebore 129.

The arms 116 and 117 include inwardly facing flanges 131 with downwardextending ears 132 at outer ends thereof. The flanges 131 and ears 132collectively form curved channels 134 that receive the closure 108, asdescribed below. Tool gripping indents 135 are formed on the exterior ofthe head 105.

The shank 106 is elongate and has a central axis of rotation indicatedby the reference letter B. The shank 106 has a lower body 138 with ahelically wound thread 139 wrapping thereabout. The shank body 138 isoperably threaded into a vertebra 101 in the manner shown in FIG. 18.

The shank 106 has an axially aligned upper portion or capture end 144with a cylindrically shaped surface 145 is connected to the shank body138 by a neck 147 and extends upwardly therefrom.

The sphere 107 has an outer generally spherical or at least partiallyspherical shaped surface 150 that is sized and shaped to be snugly, butrotatably received in the hemispherical seat 126. The sphere 107 has aradial non passthrough bore 155 sized and shaped to snugly, butinitially slidably receive the shank capture end 144.

The sphere 107 includes a pair of side opposed bores 157 and 158 whichare diagonally aligned and which intersect with and open into the bore155 so as to be perpendicular thereto. Furthermore, the sphere 107 hasan upper drive bore 159 that is coaxial with the bore 155 and that has apolyhedral shaped interior surface 160 that is sized and shaped toreceive an allen type driving tool or other suitably shaped tool fordriving the shank 106 into the vertebra 101, as described below.

The closure 108 is seen in FIGS. 20 and 21 and is a “slide in” typedevice. The purpose of the closure 108 is to close the channel 120 andto secure the rod member 110 in the channel 120 and against movementrelative to the head 105. The closure 108 includes a block or saddle 165with a lower cylindrically shaped surface 166 that is sized and shapedto snugly mate with the rod member 100.

Located on opposite ends of the saddle 165 are a pair of upwardlyextending ears 168 that are sized and shaped to be slidingly received inthe head channels 134. The ears 168 are spaced from a body 169 of thesaddle 165 by respective channels 170 that are curved and sized andshaped to slidingly receive the ears 132 of the head arms 116 and 117.In this manner the ears 132 and 168 overlap when the closure 108 is inthe head 105 to resist outward splaying of the arms 116 and 117.

The central body 169 of the closure 108 includes an axially aligned passthrough and threaded bore 180. The bore 180 receives a break-off setscrew 183 that has a base 184 and a break-off head 185.

The bone screw 100 parts are assembled and used in the following manner.As is seen between FIGS. 9 and 14, the shank upper portion or captureend 144 is inserted through the lower side of the lower side of the head105 and so as to extend into the chamber 122, while the sphere 107 isinserted or loaded through the channel 120 toward the cavity or chamber122. The shank upper portion 144 is inserted into the sphere bore 155.While the sphere 107 is maintained raised or in the upper portion of thehead 105, a crimping or deforming tool 190 is utilized to deform theshank 106 relative to the sphere 107, so as to lock or secure both toone another. In particular, the tool 190 has arms 191 that can be biasedby a scissors action or the like toward one another and a pair of lowercylindrical shaped studs 192 ending in points. The studs 192 are sizedand shaped to be inserted through opposed sides of the channel 120 andsimultaneously through the side bores 157 and 158 respectively in thesphere 107 so as to engage the shank capture end 144. Pressure is thenapplied through the studs 192 against the shank 106 so as to produce adeformation 193 that frictionally engages and interferes with the sphere107 and thereafter prevents removal of the sphere 107 from the shank106. While deformation is used herein to secure the retainer sphere tothe shank, it is also foreseen that the same could be accomplished bythreading the parts and screwing them together, by inserting a pinthrough the parts, by using cleats interlocking with receivers, bywelding, by adhering, or by any other suitable mechanism or composition.

After the sphere 107 is assembled onto the shank 106, a driving tool 197with a driving head 198 that is sized and shaped to fit the sphere drivebore 159 is used to drive the assembled parts into a bone, such as theillustrated vertebra 102 shown in FIG. 18.

Thereafter, a rod member is inserted into the channel 120. An upperportion of the sphere 107 extends upwardly into the channel 120 suchthat it is engaged by the rod member 110. The closure 108 is then slidsideways while saddling over the rod member 110 so that the closure ears168 seat in the head channels 134 inside the head ears 132 and therebylock the arms 116 and 117 against outward splaying.

The set screw 183 is then inserted into the closure bore 180 and torqueduntil a preselected torque is reached at which time the set screw head185 breaks from the body 184, as seen in FIG. 20.

At this time, the set screw 184 exerts pressure against the rod member110 which in turn exerts pressure against the sphere 107 so that thesphere 107 and attached shank 106 are frictionally locked in placerelative to the head 105. In particular, before the set screw 184 istightened, the head 105 can be rotated or swivelled relative to theshank 106 and sphere 107 assemblage, so as to find an optimal positionfor insertion of the rod member 110. After the set screw 184 istightened, the shank 106 and sphere 107 assemblage is locked in positionrelative to the head 105.

The bone screw 100 can be removed by removing the set screw base 184after which the closure 108 can be taken from the head 105. The rodmember 110 can then be removed from the head 105 and the shank 106unscrewed from the vertebra 102.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

What is claimed is:
 1. A pivotal bone anchor assembly for securing anelongate rod to a bone via a closure top, the pivotal bone anchorassembly comprising: a shank having longitudinal axis and a capture endopposite a threaded end, the capture end having a partial sphericalouter surface; a receiver having a top portion with a unitary base, thetop portion configured to receive the elongate rod in an upper channel,the base including a cavity communicating with the upper channel andwith a bottom of the receiver through a lower opening, the cavity atleast partially defined by a partial spherical lower mating surface; anda retainer positionable within the receiver cavity and having a partialspherical outer surface that is at least partially mateable with thereceiver cavity partial spherical lower mating surface, the retainerconfigured to capture the shank capture end upon uploading of the shankcapture end through the receiver lower opening, with at least a portionof the shank capture end partial spherical outer surface extending abovea top surface of the retainer after capture by the retainer, whereinafter the shank capture end is captured by the retainer, the shank isindependently rotatable around the shank longitudinal axis relative tothe retainer and the retainer is pivotable in at least one plane withrespect to the receiver prior to the closure being locked by the closuretop.
 2. The pivotal bone anchor assembly of claim 1, wherein thereceiver cavity includes an upper larger portion sized and shaped toallow expansion of the retainer during the capture of the shank captureend.
 3. The pivotal bone anchor assembly of claim 1, wherein thereceiver cavity further comprises a first region at least partiallydefined by the partial spherical lower mating surface and a secondregion being larger than the first region and located axially above thefirst region, and wherein an uploading of the shank capture end throughthe receiver lower opening causes the retainer to resiliently expandaround the shank capture end, with such expansion operably occurring inthe second region to capture the shank capture end, thereafter the shankcapture end and retainer being movable downward into the first regionand configured for pivotal engagement between the retainer and thereceiver cavity partial spherical lower mating surface.
 4. The pivotalbone anchor assembly of claim 1, wherein the retainer is configured tosnap on and capture the shank capture end during an upward movement ofthe shank capture end within the receiver cavity.
 5. The pivotal boneanchor assembly of claim 1, wherein after the shank capture end iscaptured by the retainer, the retainer is configured to pivot inmultiple planes relative to the receiver during positioning of the shankwithin the assembly.
 6. The pivotal bone anchor assembly of claim 1,wherein the retainer is downloaded into the receiver cavity through theupper channel prior to uploading the shank capture end through thereceiver lower opening.
 7. The pivotal bone anchor assembly of claim 1,wherein the retainer further comprises a resilient retaining ring havinga slit or slot.
 8. The pivotal bone anchor assembly of claim 1, whereinthe retainer further comprises an inner surface having a diameterbetween the top surface and a bottom surface of the retainer, thediameter of the inner surface decreasing toward the bottom surface ofthe retainer.
 9. The pivotal bone anchor assembly of claim 1, whereinthe retainer is spaced from the elongate rod when the elongate rod isreceived within the receiver upper channel.
 10. The pivotal bone anchorassembly of claim 1, wherein the retainer is axially rotatable around areceiver longitudinal axis when the retainer is engage with the receiverpartial spherical lower mating surface and prior to the assembly by theclosure top.
 11. The pivotal bone anchor assembly of claim 1, whereinthe retainer further comprises an inner surface between the top surfaceand a bottom surface of the retainer devoid of horizontally extendingridges, recesses and edges, the inner surface configured to snap on andengage with a external surface of the shank capture end that is alsodevoid of horizontally extending ridges, recesses and edges.
 12. Thepivotal bone anchor assembly of claim 11, wherein the external surfaceof the shank capture end is spaced below the partial spherical outersurface.
 13. The pivotal bone anchor assembly of claim 1, wherein thepartial spherical outer surface of the shank capture end furthercomprises a dome surface centered about the shank longitudinal axis. 14.The pivotal bone anchor assembly of claim 1, wherein the shank captureend has a driving structure formed therein.
 15. The pivotal bone anchorassembly of claim 1, wherein the shank includes a neck adjacent thecapture end having an outer curvilinear circumferential surface.
 16. Thepivotal bone anchor assembly of claim 1, wherein the shank is cannulatedalong an entire length thereof.
 17. The pivotal bone anchor assembly ofclaim 1, wherein when the shank capture end is capture by the retainer,the capture end is prevented from being moved up out of the retainer byan upward-facing surface on the capture end being in overlappingengagement with a surface on the retainer.
 18. The pivotal bone anchorassembly of claim 1, further comprising the closure top, and wherein adownward force to lock a position of the shank relative to the receiveris provided by the closure top bearing down on a top surface of theelongate rod.
 19. A pivotal bone anchor assembly for securing anelongate rod to a bone via a closure top, the pivotal bone anchorassembly comprising: a shank comprising a threaded body adapted to beimplanted into the bone and a capture end at an upper end of thethreaded body; a receiver having a longitudinal axis, an upper channeladapted to receive the elongate rod, a lower opening configured toreceive the shank capture end therethrough, and a cavity communicatingwith the upper channel and the lower opening, the upper channel, thecavity, and the lower opening being in axial alignment centered on thelongitudinal axis; and a resilient retainer non-integral with the shankand sized and shaped to be located during use in the receiver cavity andhaving an outer radius that is larger than a radius of the loweropening, the retainer configured to resiliently expand around the shankcapture end and thereafter capture the shank capture end in the receivercavity, the shank capture end having an upwardly extending portionopposite the shank body that extends above the retainer, the upwardlyextending portion configured for engagement by a driving tool, whereinthe retainer pivots with respect to the receiver after the shank captureend is captured by the retainer in the receiver cavity and prior tolocking a position of the shank relative to the receiver via the closuretop.
 20. The pivotal bone anchor assembly of claim 19, wherein the shankcapture end is axially rotatable in the retainer after the shank captureend is captured by the retainer in the receiver cavity and prior tolocking a position of the shank relative to the receiver via the closuretop.
 21. The pivotal bone anchor assembly of claim 19, wherein theretainer is configured to snap on and capture the shank capture endduring an upward movement of the shank capture end within the receivercavity.
 22. The pivotal bone anchor assembly of claim 19, wherein thereceiver cavity includes an upper larger portion sized and shaped toallow expansion of the retainer during the capture of the shank captureend.
 23. The pivotal bone anchor assembly of claim 19, wherein theretainer is downloaded into the receiver cavity through the upperchannel prior to uploading the shank capture end through the receiverlower opening.
 24. The pivotal bone anchor assembly of claim 19, whereinthe retainer further comprises a resilient retaining ring having a slitor slot.
 25. The pivotal bone anchor assembly of claim 19, wherein theretainer is spaced from the elongate rod when the elongate rod isreceived within the upper channel and secured via the closure top.
 26. Apivotal bone anchor assembly for securing an elongate rod to a bone viaa closure top, the pivotal bone anchor assembly comprising: a receiverof unitary construction including a top portion and a base, the topportion configured to receive the elongate rod in an upper channel, thebase including a cavity communicating with the upper channel and with abottom of the receiver through a lower opening, the cavity at leastpartially defined by a radiused lower seating surface, with at least aportion of the radiused lower cavity seating surface adjacent to andsurrounding the lower opening; a shank having a threaded end opposite acapture end, the capture end being sized and shaped to be received intothe receiver cavity through the receiver lower opening; and aresiliently expandable retainer positionable within the receiver cavityseparate from the shank, the retainer sized and shaped to resilientlyreceive and thereafter contractibly capture the shank capture end in thereceiver cavity, the retainer having a radiused outer surface that issized and shaped to be rotatably received on the radiused lower seatingsurface of the receiver cavity to provide pivotal motion between theretainer and the receiver cavity in at least one plane duringpositioning of the shank relative to the receiver, wherein an upperportion of the shank capture end projects above the retainer when thecapture end is captured in the receiver cavity by the retainer, andwherein the shank is rotatable about a shank longitudinal axis withrespect to and independent of the retainer after being captured in thereceiver cavity by the retainer and prior to the assembly being lockedvia the closure top.
 27. The pivotal bone anchor assembly of claim 26,wherein the retainer is configured to snap on and capture the shankcapture end during an upward movement of the shank capture end withinthe receiver cavity.
 28. The pivotal bone anchor assembly of claim 26,wherein the receiver cavity includes an upper larger portion sized andshaped to allow expansion of the retainer during the capture of theshank capture end.
 29. The pivotal bone anchor assembly of claim 26,wherein the retainer is downloaded into the receiver cavity through theupper channel prior to uploading the shank capture end through thereceiver lower opening.
 30. The pivotal bone anchor assembly of claim26, wherein the retainer further comprises a resilient retaining ringhaving a slit or slot.
 31. The pivotal bone anchor assembly of claim 26,wherein the retainer is spaced from the elongate rod when the elongaterod is received within the receiver upper channel.
 32. The pivotal boneanchor assembly of claim 26, further comprising the closure top, andwherein a downward force to lock a position of the shank relative to thereceiver is provided by the closure top bearing down on a top surface ofthe elongate rod.
 33. The pivotal bone anchor assembly of claim 26,wherein the shank capture end has a driving structure formed therein.34. The pivotal bone anchor assembly of claim 26, wherein the shank iscannulated along an entire length thereof.